Almost everyone has been driving and heard a “boom boom” coming from somewhere around them. This “boom boom” comes from a type of speaker called a subwoofer . A subwoofer, or a “sub” is in fact a complete loudspeaker. These types of speakers are dedicated to producing low pitch audio frequencies, or bass. Subwoofers are composed of one or more woofers within an enclosure[1] that is appropriate to their specifications. This enclosure housing one or more su
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bwoofers is designed to be able to withstand air pressure and also resist distortion at the same time. There is a large variety of subwoofer enclosure designs. Some include: bass reflex (with a port or a hole to radiate more air space), infinite baffle, horn-loaded, and bandpass designs. These several diff
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erent types of enclosures represent the many different and unique tradeoffs in respect to the subwoofer systems efficiency, bandwidth, size and cost. There are two main types of subwoofers: passive and active. Passive subwoofers need to have a subwoofer driver or stereo and an enclosure. They also need power from an external amplifier in order for the speakers their full potenetial. These are usually involved with car audio. Active subwoofers or powered subs, include a built in amplifier rather than an external one like passive subwoofers. There is also a great number of other subwoofers that will be discussed further on. In a sense, subwoofers began with Alexander Graham Bell and his creation of the telephone. He discovered in 1876 that when sound pressure waves are generated and travel through the air to our ears, we perceive the waves as sound or even music. The first subwoofers were created in the 1960’s in order to create more bass response in home stereo systems. The very first subwoofer enclosure that was made for home use was made by New Technology Enterprises. It was called the Servo Statik 1. It was made as a prototype in 1966 in a garage by a physicist named Arnold Nudell and an airline pilot named Cary Christie. It was offered for sale at 1795 dollars. The two men later made a new investment and founded the audio company known as Infinity. Subwoofers became far more popular and fell into the popular consciousness in the 1970s. This occurred because of the introduction of Sensurround, which had just been developed for movies such as Earthquake. These movies involved large destruction and earthshaking events which when being placed with Sensurround, produced loud low-frequency sounds through large subwoofers. The invention of the compact cassette and the compact disc in the 1980s allowed for easier reproduction of deep and loud bass. Beforehand, the measures of the bass and depth of volume was limited by the ability of a phonograph record stylus to track a groove. Another invention that gave great aid to subwoofers involved DVDs. DVDs began to be increasingly recorded with "surround sound" processes. These processes included a low-frequency effects (LFE) channel, which could be heard using the subwoofer in home theater systems. Subwoofers then grew in popularity in the 1990s as they became increasingly popular in home stereo systems, custom car audio installations, and in PA systems. At the turn of the century, subwoofers became highly common when it came to sound systems in clubs and concerts as well as many other kinds of loud attractions. Another one of the first subwoofers was developed during the late 1960s by Ken Kreisel. Ken Kreisel was the former president of the Miller & Kreisel Sound Corporation in Los Angeles. Kreisel had a business partner named Jonas Miller who owned a high-end audio store in Los Angeles. Miller explained to Kreisel that a good amount of customers and people that had purchased some of the store's top of the line electrostatic speakers had been complaining about the electrostatics of the speakers lacking in bass. After hearing this, Kreisel designed and created a different kind of powered subwoofer that was dedicated to producing only low frequencies. Specifically, the frequencies that were much too low for the initial electrostatic speakers to produce. Infinity also developed a full range electrostatic speaker system in the 1960’s. This system of theirs also used a woofer to produce lower frequencies and cover the range that its electrostatic arrays could not.
Design and Parts of a Subwoofer
Now, subwoofers are common all around and are a highly essential part of an impressive sound system. For a subwoofer to work an amplifier must turn your music into alternate current electricity. Once connected to a speaker the alternate current electricity makes the speaker cone move in and out creating the sound pressure waves travel through the air to your ears, where you perceive it as sound. The motion of the speakers face and moving parts is made possible by the attraction and the pulsation of an electro magnet to a permanent magnet. An electro magnet is in fact only a magnet when the electricity from an amp runs through a coil of wire which is called the voice coil. The thing that makes an electro magnet special is that its polarity can either be positive or negative but all depending on the electrical charge that is ran through it. When negative electricity travels through the voice coil, the electro magnet is attracted to the permanent magnet and it moves towards it. When the charge is reversed to positive, the voice coil pushes away from the permanent magnet because the two magnets are no longer attracted to one another. This up and down movement that the voice coil performs is directly relevant to the polarity of the alternating current electricity that is sent to it from the amplifier. A cone is then placed on the voice coil because without it, the movement of the voice coil up and down would hardly remove any air. The movement of the voice coil with this cone creates pressure waves that travel through space and vibrate your ear drums. This creates perceivable sound like Alexander Graham Bell discovered. Further parts are necessary to keep the cone in place and still let it move in and out. A flexible part called the surround is attached to the top of the cone. Another flexible part, called the spider, aligns the bottom of the cone. The purpose of the spider is to allow the cone to move in and out without it moving out of place or back and forth. Another part that is used to keep the cone in place is a front gasket. Further stability is acquired by placing a separate plastic part called the spider landing to the outside edge of the spider. A top plate is added in order to make the permanent magnet more effective. The top plate is a steel ring that concentrates this magnetic force into a smaller area. Most of the magnetic force is concentrated in a small gap between the top plate and a cylindrical part called the pole piece. This pole piece extends the magnetic field and dissipates heat from the voice coil. The rest of the magnetic force heat is extended through the pole piece to the back plate which extends the force even more and concentrates the magnetic field. The shape of this assembly is highly important to the performance of the speaker. In order to transfer the audio to the voice coil, a connection is made through flexible wires called tinsel leads. These are then attached to a terminal where the speaker wires from an amplifier are connected. Lastly, these parts are then all held together by what’s called the basket which also provides a phalange for mounting the speaker.
Creation of the Electromagnet and Its Use With Loudspeakers
As stated before, subwoofers function by the use of an electromagnet that moves back and
forth when alternating currents of electricity from music pass through it. Perhaps the most integral part of a subwoofer that causes it to function is its use of an electromagnet. This is important because when an electro magnet comes in contact with alternating electric currents, its polarity then changes and the electro magnet pulls and repels depending on the current that it comes in contact with. Subwoofers use this so that the magnet may change from positive and negative in polarity and thus move. An electromagnet is simply a coil of wire. This wire is usually wound around an iron core but is also capable of being wrapped around an air core which would then make it not an electromagnet, but in fact a solenoid. When a DC current passes through the electromagnet, it gains energy and forms a magnetic field that is similar to that of a permanent magnet. The strength and density of the magnetic field is proportional to the amount of energy that is traveling through the electromagnets wires. The polarity of the electromagnet is dependent on the direction of the current. With a DC current, the current travels in the direction that leads North. Thus, the electromagnetic field faces upward and pulls objects towards it. These kinds of electromagnets, using DC currents, are often used to pick objects up. When connected to an AC current, an electromagnet’s flux density changes as the current changes. When this happens, the polarity of the magnet also changes as the current changes and its polarity then reverses direction throughout every half cycle. Unlike DC electromagnets, AC electromagnets can be used to demagnetize objects. This can be used for such things as TV screens or vcr tapes and also be used to hold objects. However, due to the property of electric circuit of the electromagnet, or inductance, the AC current that flows will actually be less when compared to a DC voltage. The most important thing of an electromagnet is the capabilities and manipulation that it allows. For example, when using an electromagnet there is an ability to control the magnetic density’s strength, while also being able to change its polarity and the shape of its magnetic field. It is possible to control the strength of the magnetic density by changing the extent of the current that is flowing throughout the coil. The direction of the flow of the current is what changes allows manipulation and control of the polarity of the field. Lastly, controlling the shape of the field is achieved by also controlling the shape of what the wire is wrapped around. Simply, the shape of the iron core manipulates the overall shape of the magnetic field. Electromagents are used in many other different devices such as motors, relays, hard disks, generators, and even large magnets for picking up and moving metal scraps in scrapyards. A Danish scientist by the name of Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields. Four years later, a British scientist named William Sturgeon invented the electromagnet. This first electromagnet was quite simple. Sturgeon developed a horseshoe-shaped piece of iron that had bare copper wire wound about it. In order to provide insulation, Sturgeon varnished the iron to insulate it from the windings. When a current passed through the coil, the iron developed energy and became magnetized. The iron then began to attract other pieces of iron but when the current discontinued, the iron lost its magnetic properties. Sturgeon then discovered an impressive capability of the electromagnet in that even though it only weighed a mere seven ounces, it could life about nine pounds under the current provided from a single cell battery. Although Sturgeon had made a great achievement and created an impressive invention, he also had avery important flaw within his creation. This flaw was that Sturgeon's magnets were rather weak due to the uninsulated wire that he used. This wire could only be wrapped in a single spaced out layer around the core which in turn, limited the number of turns that could be made with the wire. A few years later, in 1827, an American scientist named Joseph Henry improved and popularized the electromagnet. Henry improved the electromagnet by using wire that was insulated by silk thread. By doing so, he was able to wind multiple layers of wire on cores. This created far more powerful magnets with thousands of turns of wire, including one that could support 2,063 lb. Although the electromagnet proved to be an astonishing invention, the first major use for electromagnets was in fact involved with telegraph sounders. Speakers are created using a one layer coil of wire and a tube which is then placed within a magnetic field. The one layer coil of wire is wound about a tube and then placed into the magnetic field. The end of the tube is attached to the center of the speakers cone, which is usually made of paper. When a current is passed throughout the coil, a force is created on the coil and causes it to energize. This then causes it and the tube to move within the magnetic field, either up or down from a permanent magnet depending on the polarity that is generated within the coil from the alternating current. When the current reverses direction, the coils polarity is changed causing it and the tube to move in the opposite direction.
Subwoofer Enclosures
However, there are a few other things a subwoofer needs to function. The first thing that a subwoofer needs in order it to produce sound is a stereo or driver that will send certain currents from music to the subwoofer. Without these certain alternating currents of electricity from music, the subwoofer wouldn’t have any music to play to begin with. The next thing a subwoofer needs is an amp. An amp takes the alternating currents produced from the stereo and it then amplifies the current in order to provide more power for the subwoofer. With more power comes more bass and sound. This is how subs get the power to generate the loud and deep bass that they are known for. A subwoofer then needs an enclosure which may be made of particle board or other very dense woods or sometimes even a thick plexiglass. There are many different types of subwoofer enclosures. They may be completely sealed, for deep and precise bass. A sealed box is an airtight enclosure, with a subwoofers face facing outward while the cone and base of the speaker is sealed inside. A sealed box is the best choice for any music that calls for accurate bass. With a sealed enclosure, you can expect flat response with deep bass extension while also being provided with excellent power handling. Power handling is very important in tuning your subwoofer the way you want it to produce bass. Without proper power handling, a person could easily have their subwoofer putting out more bass than its meant to handle and possibly blow the speaker and cause it to cease fuctioning. An amplifier with ample wattage is ideal for these enclosures in order to produce the best performance. Another type of subwoofer is a ported box. Ported boxes use a vent, which is called a port, to reinforce low bass response. With a ported box, a person gets more output than they would from a sealed box at any given amplifier wattage. Ported boxes are often preferred by people who are wanting to use them
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for any hard driving music such as heavy metal. Although they can produce deeper bass and require less power than sealed boxes, ported boxes must be much larger than a sealed enclosure to do so. There are also two other types of subwoofer enclosure designs: bandpass boxes and free air sytems. Bandpass boxes provide a maximum amount of what subwoofer enthusiasts call “slam”, meaning the most amount of hard hitting bass. Bandpass boxes are a special type of ported box designed for the greatest amount of this so called “slam”. For the design, the subwoofer is mounted inside a dual-chambered box, with one chameber sealed while the other chamber is ported. The sound waves produced by the subwoofer derive from the ported side. These soundwaves produce a sound that comes out of the port which is very loud while remaining within a narrow frequency range. Since bandpass design systems are incredibly effiecient within this range,
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they tend to make a very loud and deep amount of bass. Or as subwoofer enthusiasts would call, “boom” or “slam. This loud, aggressive sound is idea for music genres such as hard rock, rap, and reggae. However, not all subwoofers work well in bandpass boxes and produce this “slam” that so many subwoofer fanatics want. It is important for a person to check whether their subwoofer will work with this design before attempting to have it placed in a banpass designed enclosure. Lastly, is the design of a free-air system. A free air system consists of subwoofers that are mounted to a board that is then attached to the rear deck or placed in an automobile against the rear seat. With this design, the trunk of the automobile functions as an enclosure which houses the subwoofer while it also isolates sound from the back of the speaker. This then solves the problem of sound cancellation of subwoofers without an enclosure. While free-air systems save space, they also have a flat frequency response. Because of this, not just any subwoofer can be used for this system. The subwoofer must be specifically designed for the use of a free air system. The free air system’s lack of using a box makes them more expedient when it comes to installation. Although, the power handling levels of a free air system are usually much lower than the other types of fully enclosed sytems.
Subwoofer Manufacturers
There are many different manufacturers of speakers and subwoofers. Some of the top end brands involve Kicker, Rockford Fosgate, Kenwood, Alpine, MTX, Blaupunkt and many others. With these many different manufacturers comes many different types of subwoofers. Kicker for example, produces the worlds only square faced subwoofer[2] , whereas all other subs are designed with a circula
Kicker Classic Round Face Solobaric Subwoofer. Image courtesy of www.bikersfinder.com
Kicker Square Faced L7 Solobaric Subwoofer. Image courtesy of www.productwiki.com
r face. This subwoofer is known as one of the loudest and most powerful subwoofers on the market. Even the Kicker website claims that the speaker’s power and bass output is “not for the faint of heart”. Another unique subwoofer is produced by a company named Bazooka. This unique subwoofer uses the design of a tube subwoofer. These subwoofers are built an enclosure that is infact a tube and actually houses an amplifier within the same enclosure. These subs are unique in that only a few other companies produce this type of enclosure. They are also said to be very power efficient because of their design. The enclosure focuses all of the energy provided to it on a very narrow frequency which allows for more focus of power at the times where most music calls for its loud moments of bass. These enclosures are also ported which works to further amplify the system response around the bass port resonant frequency as compared to a typical ported enclosure. This design also brings the bass port all the way to the front to exit in the same plane as the subwoofer. Usually a bass port tuned for a quarter wavelength and exiting in the same plane as the original speaker driver helps to improve the subwoofer’s response in a vented or ported system. This works to bring it closer to the response of a sealed system, while having the 3db gain advantage of the ported design.
Subwoofer System DIY's
Many car audio and subwoofer enthusiasts feel the temptation at some point to build their own speaker system or enclosure for their subwoofers[3] . These people often plan to be quite successful and expect that they’ll create a quite impressive speaker system while having started from a small amount of knowledge. However, this often does not occur and people are left baffled by their lack of success. Or perhaps they realize their major mistake and correct it. At any rate, this occurs because a great amount of detail and knowledge is required in order for a person to construct an impressive enclosure for their speaker system, let alone having it be p
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roper to their speakers. It is important for the person to begin with a project that is just a little greater than their own grasp of knowledge so as to learn along the way, but not be overwhelmed by the task at hand. Although some do it yourself projects turn out well, failure to recognize to not have your reach exceed your grasp could result in a mediocre system. Or possibly even a system that doesn’t work at all, resulting in a great amount of time and money that went to waste. If someone is a beginner, it is a good idea for them to choose and buy one of readily available kits or a system that has already been designed[4] . These are a good choice because the work is easily explained to you with the proper materials, along with the chance of failure based at a minimal level as opposed to starting from scratch. Perhaps the most important and primary part of conducting a do it yourself project is selecting the driver for your system. Working from a set of plans or an ordered kit can be a good idea because this has often already been done. Another luxury of using a kit is that many kits offer some versatility to the speaker system and its components. For example, a great number of different drivers can be chosen to fit within the same cutout of the panel that is used within the kit. Because of this, a person has the option of and may wish to switch it up and choose alternatives. If a person is building from scratch, selecting the proper driver is an integral part of the process. Luckily, selecting the proper driver for the system you want is not near as strenuous as you’d think. First off, a person must determine what the main purpose of their speaker or speakers is. They must consider whether they are building this enclosure for an automobile, a home system, or possibly just for a greater amount of volume in their music. The majority of people use their speakers for both an automobile and music or the same for a home theater system and music. Here are the proper recommendations that the person needs follow in their pursuit of an impressive system: · A home theater system requires at least 6 speakers. These 6 speakers consist of two main left and right speakers, a center channel speaker for the front, two rear channel speakers, and lastly a subwoofer. For home theater systems, the control of the sound field lies with the recording engineers. Thus, the five rear and main speakers ought to sound quite close to one another. It is also important to keep the speakers simple and cost effective, since there are so many of them. If the person doesn't want all five to be th
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e same, it is important that they try and make the front three alike as well as the back two so that both will have a common sound with one another. An important thing to make sure to do for the front three is to keep them magnetically shielded so that they will keep from interfering with the tv. All of the speakers should have their response around 80Hz so that the subwoofer will take over. After all, one of the most impressive parts of a home audio system is the bass. · The majority of music systems are still stereo for the most part. Even though a good portion of audio discs and motion picture soundtracks have many channels alike with home theaters, the majority of the focus should placed upon the two speakers in the front. Simply because of the option for other channels. You may choose to use a full range system or focus on subwoofers instead. If a person chooses to focus on a subwoofer, there is one necessity out of two choices that they must have. The person can choose between using an electronic crossover or also one of the readily available basic amplifiers. These readily available amplifiers is a good choice because they are deliberately built to be attached or mounted within the subwoofer enclosure for this specific purpose. Some of the many companies that produce amplifiers are Madisound and Meniscus, among many others that also focus on actual speaker design rather than powering them. · Combining the above systems involves balancing the above requirements. To design a system such as this, the person must determine what percentage of their system will be used for music and what percentage will be used for home theater. As the numbers become greater on either side of fifty percent, fewer compromises will need to be made. Systems that use each application about fifty percent of the time will require more compromises. These systems often use two very high quality front speakers with a center channel speaker of the same "sound". The two front main speakers may be placed at a distance from the TV screen to a point where they may no longer need magnetic shielding. However, the center channel speaker will need to be shielded. Rear channel speakers in this system are somewhat unimportant, but should still have the same sound as the front speakers. A subwoofer is recommended, although most home theater receivers will allow you to avoid a subwoofer. Second, a basic design must be chosen. Doing so will determine the amount of drivers and their parameters. It is important to remember though that the more receivers you use, the easier it will be to mess something up. Two-way designs are the simplest and can sound quite good, as long as they use the correct driver. Three-way designs call for much more precision in fitting all the pieces so as to make them alike. Four-way designs are far more complex and confusing. Often, these will have crossovers in the middle of the critical musical range of 300-3,000 Hz, which makes driver matching much more critical.
Hoffman's Iron Law
There is another thing that a new speaker builder must learn. It is a fundamental and key aspect of speaker enclosure design that is known as "Hoffman's Iron Law"[5] . Developed and created in the 1960’s by Anthony Hoffman, it is a mathematical formula. However, this equation was later tweaked and enhanced for the better by Thiele and Small. Now, these men’s work is said to have formed the basis of the design of all subwoofer and loudspeaker systems that exist to this day. This formula, in short, explains that the proficiency that a subwoofer system may be capable of is directly proportional to its cabinet volume and the cube of its cutoff frequency. The cutoff frequency is the lowest frequency that the subwoofer can successfully reproduce while remaining useful. The most easily noticed idea is in order to change the cutoff frequency, in this case by a factor of two or to make the subwoofers capability of producing deeper bass even more impressive while retaining the systems same efficiency, a person would need to increase the enclosure by a great amount. For example, to bring the subwoofer systems cutoff frequency from 40 Hz to 20 Hz, while maintaining its initial efficiency, a person would need to increase the enclosure system volume by about eight times. Simply put, in order to generate lower frequencies while maintain the same outputlevel, a much larger box is needed. Box size is by far not the only significant variable. A small box can be used but in return, a much lower efficiency must be accepted. With the intention of maintaining the same sound pressure level, a person must use a very large amplifier for a greater amount of power and a driver that can handle this great increase in power while still being able to move lots of air. Additionally, this system must be able to accomplish all of this with as little distortion as possible. This distortion derives from power compression, an occurrence where the driver's voice coil begins to heat up throughout its continuous use of power which then yields a non-linear relationship between the acoustical power that is going out and the electrical power that is traveling in. Because of this, the systems efficiency and tendency of distortion is easily aggravated. Bandwidth is another quite important variable in speaker systems efficiency however, it is not often mentioned. By using a bandpass design, a person can display the perception of having violated Hoffman's Iron Law. This is because by using a bandpass design, a person can provide a great amount of bass that is mainly across a significantly limited bandwidth. With many bandpass designs, this impressive bass is often generated around a single frequency. This production of bass on a single frequency is referred to as "one-note bass". This can shake your furniture and room and impress your guests while also possibly being okay for sound effects in things such as action movies. However, when using this design, you can expect a great amount of accuracy when listening to music with an abundance of content containing low bass. All together, a systems capabilitiy of producing low frequencies, the enclosure size, and the systems overall effieciency create integral parts of a system’s design. In order to enhance any of the three, some sacrifices must be made. In order to enhance one thing, something from the other two must be given up. The most important of these sacrifices is box size since it is the most sensitive of the three. Because of this, the often bottom line that people go with is the plan on using the largest box they can use with atleast some amount of comfortability. This can explain why subwoofers are so popular to some extent in that they can be large while also being hidden from view, and sometimes even have their own built in source of power or amplifier.
Law's Governing Use of Subwoofers
Because of the loud and ear splitting amount of noise that subwoofers can make, there have been many laws made against subwoofers and their use. This is because people have began to get tired of people ignorantly blaring their music and abusing their music system at the cost of comfortability for others. People often claim that subwoofers are too much of a distraction while driving and that they can lead to car accidents. They also claim that they violate the laws of disturbing the peace, specifically at night when people may drive through neighborhoods having their music very loud to the point where they might wake up the sleeping homeowners. Because of this, laws have been made against people having their subwoofers playing at a certain volume. Failure to obey these laws often results in the person receiving a fine or ticket the same as they would if they were speeding. Because of this, the luxury of having your vehicle or home audio system be able to generate such audio with such power, comes with a significant amount of responsibility. Link To Presentation:https://docs.google.com/leaf?id=0B6BRmP-QHNRaY2E0MWRlY2YtNmU0My00MGExLWE0YWQtYzRkNGQyMTUwZGZi&hl=en&authkey=CJn327EC
Table of Contents
Intro to Subwoofers and Their Creation
Almost everyone has been driving and heard a “boom boom” coming from somewhere around them. This “boom boom” comes from a type of speaker called a subwoofer . A subwoofer, or a “sub” is in fact a complete loudspeaker. These types of speakers are dedicated to producing low pitch audio frequencies, or bass. Subwoofers are composed of one or more woofers within an enclosure[1] that is appropriate to their specifications. This enclosure housing one or more su
Another one of the first subwoofers was developed during the late 1960s by Ken Kreisel. Ken Kreisel was the former president of the Miller & Kreisel Sound Corporation in Los Angeles. Kreisel had a business partner named Jonas Miller who owned a high-end audio store in Los Angeles. Miller explained to Kreisel that a good amount of customers and people that had purchased some of the store's top of the line electrostatic speakers had been complaining about the electrostatics of the speakers lacking in bass. After hearing this, Kreisel designed and created a different kind of powered subwoofer that was dedicated to producing only low frequencies. Specifically, the frequencies that were much too low for the initial electrostatic speakers to produce. Infinity also developed a full range electrostatic speaker system in the 1960’s. This system of theirs also used a woofer to produce lower frequencies and cover the range that its electrostatic arrays could not.
Design and Parts of a Subwoofer
Now, subwoofers are common all around and are a highly essential part of an impressive sound system. For a subwoofer to work an amplifier must turn your music into alternate current electricity. Once connected to a speaker the alternate current electricity makes the speaker cone move in and out creating the sound pressure waves travel through the air to your ears, where you perceive it as sound. The motion of the speakers face and moving parts is made possible by the attraction and the pulsation of an electro magnet to a permanent magnet. An electro magnet is in fact only a magnet when the electricity from an amp runs through a coil of wire which is called the voice coil. The thing that makes an electro magnet special is that its polarity can either be positive or negative but all depending on the electrical charge that is ran through it. When negative electricity travels through the voice coil, the electro magnet is attracted to the permanent magnet and it moves towards it. When the charge is reversed to positive, the voice coil pushes away from the permanent magnet because the two magnets are no longer attracted to one another. This up and down movement that the voice coil performs is directly relevant to the polarity of the alternating current electricity that is sent to it from the amplifier. A cone is then placed on the voice coil because without it, the movement of the voice coil up and down would hardly remove any air. The movement of the voice coil with this cone creates pressure waves that travel through space and vibrate your ear drums. This creates perceivable sound like Alexander Graham Bell discovered. Further parts are necessary to keep the cone in place and still let it move in and out. A flexible part called the surround is attached to the top of the cone. Another flexible part, called the spider, aligns the bottom of the cone. The purpose of the spider is to allow the cone to move in and out without it moving out of place or back and forth. Another part that is used to keep the cone in place is a front gasket. Further stability is acquired by placing a separate plastic part called the spider landing to the outside edge of the spider. A top plate is added in order to make the permanent magnet more effective. The top plate is a steel ring that concentrates this magnetic force into a smaller area. Most of the magnetic force is concentrated in a small gap between the top plate and a cylindrical part called the pole piece. This pole piece extends the magnetic field and dissipates heat from the voice coil. The rest of the magnetic force heat is extended through the pole piece to the back plate which extends the force even more and concentrates the magnetic field. The shape of this assembly is highly important to the performance of the speaker. In order to transfer the audio to the voice coil, a connection is made through flexible wires called tinsel leads. These are then attached to a terminal where the speaker wires from an amplifier are connected. Lastly, these parts are then all held together by what’s called the basket which also provides a phalange for mounting the speaker.
Creation of the Electromagnet and Its Use With Loudspeakers
As stated before, subwoofers function by the use of an electromagnet that moves back and
An electromagnet is simply a coil of wire. This wire is usually wound around an iron core but is also capable of being wrapped around an air core which would then make it not an electromagnet, but in fact a solenoid. When a DC current passes through the electromagnet, it gains energy and forms a magnetic field that is similar to that of a permanent magnet. The strength and density of the magnetic field is proportional to the amount of energy that is traveling through the electromagnets wires. The polarity of the electromagnet is dependent on the direction of the current. With a DC current, the current travels in the direction that leads North. Thus, the electromagnetic field faces upward and pulls objects towards it. These kinds of electromagnets, using DC currents, are often used to pick objects up. When connected to an AC current, an electromagnet’s flux density changes as the current changes. When this happens, the polarity of the magnet also changes as the current changes and its polarity then reverses direction throughout every half cycle. Unlike DC electromagnets, AC electromagnets can be used to demagnetize objects. This can be used for such things as TV screens or vcr tapes and also be used to hold objects. However, due to the property of electric circuit of the electromagnet, or inductance, the AC current that flows will actually be less when compared to a DC voltage. The most important thing of an electromagnet is the capabilities and manipulation that it allows. For example, when using an electromagnet there is an ability to control the magnetic density’s strength, while also being able to change its polarity and the shape of its magnetic field. It is possible to control the strength of the magnetic density by changing the extent of the current that is flowing throughout the coil. The direction of the flow of the current is what changes allows manipulation and control of the polarity of the field. Lastly, controlling the shape of the field is achieved by also controlling the shape of what the wire is wrapped around. Simply, the shape of the iron core manipulates the overall shape of the magnetic field. Electromagents are used in many other different devices such as motors, relays, hard disks, generators, and even large magnets for picking up and moving metal scraps in scrapyards. A Danish scientist by the name of Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields. Four years later, a British scientist named William Sturgeon invented the electromagnet. This first electromagnet was quite simple. Sturgeon developed a horseshoe-shaped piece of iron that had bare copper wire wound about it. In order to provide insulation, Sturgeon varnished the iron to insulate it from the windings. When a current passed through the coil, the iron developed energy and became magnetized. The iron then began to attract other pieces of iron but when the current discontinued, the iron lost its magnetic properties. Sturgeon then discovered an impressive capability of the electromagnet in that even though it only weighed a mere seven ounces, it could life about nine pounds under the current provided from a single cell battery. Although Sturgeon had made a great achievement and created an impressive invention, he also had avery important flaw within his creation. This flaw was that Sturgeon's magnets were rather weak due to the uninsulated wire that he used. This wire could only be wrapped in a single spaced out layer around the core which in turn, limited the number of turns that could be made with the wire. A few years later, in 1827, an American scientist named Joseph Henry improved and popularized the electromagnet. Henry improved the electromagnet by using wire that was insulated by silk thread. By doing so, he was able to wind multiple layers of wire on cores. This created far more powerful magnets with thousands of turns of wire, including one that could support 2,063 lb. Although the electromagnet proved to be an astonishing invention, the first major use for electromagnets was in fact involved with telegraph sounders. Speakers are created using a one layer coil of wire and a tube which is then placed within a magnetic field. The one layer coil of wire is wound about a tube and then placed into the magnetic field. The end of the tube is attached to the center of the speakers cone, which is usually made of paper. When a current is passed throughout the coil, a force is created on the coil and causes it to energize. This then causes it and the tube to move within the magnetic field, either up or down from a permanent magnet depending on the polarity that is generated within the coil from the alternating current. When the current reverses direction, the coils polarity is changed causing it and the tube to move in the opposite direction.
Subwoofer Enclosures
However, there are a few other things a subwoofer needs to function. The first thing that a subwoofer needs in order it to produce sound is a stereo or driver that will send certain currents from music to the subwoofer. Without these certain alternating currents of electricity from music, the subwoofer wouldn’t have any music to play to begin with. The next thing a subwoofer needs is an amp. An amp takes the alternating currents produced from the stereo and it then amplifies the current in order to provide more power for the subwoofer. With more power comes more bass and sound. This is how subs get the power to generate the loud and deep bass that they are known for. A subwoofer then needs an enclosure which may be made of particle board or other very dense woods or sometimes even a thick plexiglass. There are many different types of subwoofer enclosures. They may be completely sealed, for deep and precise bass. A sealed box is an airtight enclosure, with a subwoofers face facing outward while the cone and base of the speaker is sealed inside. A sealed box is the best choice for any music that calls for accurate bass. With a sealed enclosure, you can expect flat response with deep bass extension while also being provided with excellent power handling. Power handling is very important in tuning your subwoofer the way you want it to produce bass. Without proper power handling, a person could easily have their subwoofer putting out more bass than its meant to handle and possibly blow the speaker and cause it to cease fuctioning. An amplifier with ample wattage is ideal for these enclosures in order to produce the best performance. Another type of subwoofer is a ported box.
Ported boxes use a vent, which is called a port, to reinforce low bass response. With a ported box, a person gets more output than they would from a sealed box at any given amplifier wattage. Ported boxes are often preferred by people who are wanting to use them
Bandpass boxes provide a maximum amount of what subwoofer enthusiasts call “slam”, meaning the most amount of hard hitting bass. Bandpass boxes are a special type of ported box designed for the greatest amount of this so called “slam”. For the design, the subwoofer is mounted inside a dual-chambered box, with one chameber sealed while the other chamber is ported. The sound waves produced by the subwoofer derive from the ported side. These soundwaves produce a sound that comes out of the port which is very loud while remaining within a narrow frequency range. Since bandpass design systems are incredibly effiecient within this range,
Subwoofer Manufacturers
There are many different manufacturers of speakers and subwoofers. Some of the top end brands involve Kicker, Rockford Fosgate, Kenwood, Alpine, MTX, Blaupunkt and many others. With these many different manufacturers comes many different types of subwoofers. Kicker for example, produces the worlds only square faced subwoofer[2] , whereas all other subs are designed with a circula
Subwoofer System DIY's
Many car audio and subwoofer enthusiasts feel the temptation at some point to build their own speaker system or enclosure for their subwoofers[3] . These people often plan to be quite successful and expect that they’ll create a quite impressive speaker system while having started from a small amount of knowledge. However, this often does not occur and people are left baffled by their lack of success. Or perhaps they realize their major mistake and correct it. At any rate, this occurs because a great amount of detail and knowledge is required in order for a person to construct an impressive enclosure for their speaker system, let alone having it be p
Perhaps the most important and primary part of conducting a do it yourself project is selecting the driver for your system. Working from a set of plans or an ordered kit can be a good idea because this has often already been done. Another luxury of using a kit is that many kits offer some versatility to the speaker system and its components. For example, a great number of different drivers can be chosen to fit within the same cutout of the panel that is used within the kit. Because of this, a person has the option of and may wish to switch it up and choose alternatives. If a person is building from scratch, selecting the proper driver is an integral part of the process. Luckily, selecting the proper driver for the system you want is not near as strenuous as you’d think.
First off, a person must determine what the main purpose of their speaker or speakers is. They must consider whether they are building this enclosure for an automobile, a home system, or possibly just for a greater amount of volume in their music. The majority of people use their speakers for both an automobile and music or the same for a home theater system and music. Here are the proper recommendations that the person needs follow in their pursuit of an impressive system:
· A home theater system requires at least 6 speakers. These 6 speakers consist of two main left and right speakers, a center channel speaker for the front, two rear channel speakers, and lastly a subwoofer. For home theater systems, the control of the sound field lies with the recording engineers. Thus, the five rear and main speakers ought to sound quite close to one another. It is also important to keep the speakers simple and cost effective, since there are so many of them. If the person doesn't want all five to be th
· The majority of music systems are still stereo for the most part. Even though a good portion of audio discs and motion picture soundtracks have many channels alike with home theaters, the majority of the focus should placed upon the two speakers in the front. Simply because of the option for other channels. You may choose to use a full range system or focus on subwoofers instead. If a person chooses to focus on a subwoofer, there is one necessity out of two choices that they must have. The person can choose between using an electronic crossover or also one of the readily available basic amplifiers. These readily available amplifiers is a good choice because they are deliberately built to be attached or mounted within the subwoofer enclosure for this specific purpose. Some of the many companies that produce amplifiers are Madisound and Meniscus, among many others that also focus on actual speaker design rather than powering them.
· Combining the above systems involves balancing the above requirements. To design a system such as this, the person must determine what percentage of their system will be used for music and what percentage will be used for home theater. As the numbers become greater on either side of fifty percent, fewer compromises will need to be made. Systems that use each application about fifty percent of the time will require more compromises. These systems often use two very high quality front speakers with a center channel speaker of the same "sound". The two front main speakers may be placed at a distance from the TV screen to a point where they may no longer need magnetic shielding. However, the center channel speaker will need to be shielded. Rear channel speakers in this system are somewhat unimportant, but should still have the same sound as the front speakers. A subwoofer is recommended, although most home theater receivers will allow you to avoid a subwoofer.
Second, a basic design must be chosen. Doing so will determine the amount of drivers and their parameters. It is important to remember though that the more receivers you use, the easier it will be to mess something up. Two-way designs are the simplest and can sound quite good, as long as they use the correct driver. Three-way designs call for much more precision in fitting all the pieces so as to make them alike. Four-way designs are far more complex and confusing. Often, these will have crossovers in the middle of the critical musical range of 300-3,000 Hz, which makes driver matching much more critical.
Hoffman's Iron Law
There is another thing that a new speaker builder must learn. It is a fundamental and key aspect of speaker enclosure design that is known as "Hoffman's Iron Law"[5] . Developed and created in the 1960’s by Anthony Hoffman, it is a mathematical formula. However, this equation was later tweaked and enhanced for the better by Thiele and Small. Now, these men’s work is said to have formed the basis of the design of all subwoofer and loudspeaker systems that exist to this day.
This formula, in short, explains that the proficiency that a subwoofer system may be capable of is directly proportional to its cabinet volume and the cube of its cutoff frequency. The cutoff frequency is the lowest frequency that the subwoofer can successfully reproduce while remaining useful. The most easily noticed idea is in order to change the cutoff frequency, in this case by a factor of two or to make the subwoofers capability of producing deeper bass even more impressive while retaining the systems same efficiency, a person would need to increase the enclosure by a great amount. For example, to bring the subwoofer systems cutoff frequency from 40 Hz to 20 Hz, while maintaining its initial efficiency, a person would need to increase the enclosure system volume by about eight times. Simply put, in order to generate lower frequencies while maintain the same outputlevel, a much larger box is needed.
Box size is by far not the only significant variable. A small box can be used but in return, a much lower efficiency must be accepted. With the intention of maintaining the same sound pressure level, a person must use a very large amplifier for a greater amount of power and a driver that can handle this great increase in power while still being able to move lots of air. Additionally, this system must be able to accomplish all of this with as little distortion as possible. This distortion derives from power compression, an occurrence where the driver's voice coil begins to heat up throughout its continuous use of power which then yields a non-linear relationship between the acoustical power that is going out and the electrical power that is traveling in. Because of this, the systems efficiency and tendency of distortion is easily aggravated. Bandwidth is another quite important variable in speaker systems efficiency however, it is not often mentioned. By using a bandpass design, a person can display the perception of having violated Hoffman's Iron Law. This is because by using a bandpass design, a person can provide a great amount of bass that is mainly across a significantly limited bandwidth. With many bandpass designs, this impressive bass is often generated around a single frequency. This production of bass on a single frequency is referred to as "one-note bass". This can shake your furniture and room and impress your guests while also possibly being okay for sound effects in things such as action movies. However, when using this design, you can expect a great amount of accuracy when listening to music with an abundance of content containing low bass.
All together, a systems capabilitiy of producing low frequencies, the enclosure size, and the systems overall effieciency create integral parts of a system’s design. In order to enhance any of the three, some sacrifices must be made. In order to enhance one thing, something from the other two must be given up. The most important of these sacrifices is box size since it is the most sensitive of the three. Because of this, the often bottom line that people go with is the plan on using the largest box they can use with atleast some amount of comfortability. This can explain why subwoofers are so popular to some extent in that they can be large while also being hidden from view, and sometimes even have their own built in source of power or amplifier.
Law's Governing Use of Subwoofers
Because of the loud and ear splitting amount of noise that subwoofers can make, there have been many laws made against subwoofers and their use. This is because people have began to get tired of people ignorantly blaring their music and abusing their music system at the cost of comfortability for others. People often claim that subwoofers are too much of a distraction while driving and that they can lead to car accidents. They also claim that they violate the laws of disturbing the peace, specifically at night when people may drive through neighborhoods having their music very loud to the point where they might wake up the sleeping homeowners. Because of this, laws have been made against people having their subwoofers playing at a certain volume. Failure to obey these laws often results in the person receiving a fine or ticket the same as they would if they were speeding. Because of this, the luxury of having your vehicle or home audio system be able to generate such audio with such power, comes with a significant amount of responsibility.
Link To Presentation: https://docs.google.com/leaf?id=0B6BRmP-QHNRaY2E0MWRlY2YtNmU0My00MGExLWE0YWQtYzRkNGQyMTUwZGZi&hl=en&authkey=CJn327EC
http://www.soundonsound.com/sos/apr07/articles/subwoofers.htm All you wanted to know about subwoofers
http://www.osd.rutgers.edu/gs/06papers/Subwoof.pdf Experiences designing and building a subwoofer
http://ldsg.snippets.org/appdx-a.php#HOFFMAN Hoffman’s Iron Law
http://www.crutchfield.com/learn/learningcenter/car/subwoofer_installation_guide.html How to install a subwoofer
http://www.kicker.com/Solo-Baric_L7 Kicker Solobaric square subwoofer
http://www.invodo.com/Kicker-How-Speakers-Work/p/S6KS0Q48 kicker video on how subwoofers work
http://www.mtx.com/caraudio/products/subwoofers/jackhammer.cfm largest subwoofer for car audio
http://en.wikipedia.org/wiki/Loudspeaker_enclosure#Infinite_baffle subwoofer enclosure wikipedia page
http://en.wikipedia.org/wiki/Subwoofer subwoofer wikipedia page
http://hometheater.about.com/cs/loudspeakers/a/aasubwoofera.htm Subwoofers-what you need to know
Electricity and Magnetism. (2001). In Grolier Incorporated, Americana Incorporated, Encylcopedia Americana Corporation, Phillipines by Grolier International, Inc., & Republic of China by Grolier International, Inc. (Eds.), Encyclopedia America (International Edition ed., Vol. 30, p. 99). Danbury, Connecticut: Grolier Incorporated. (Original work published 1829)
[[http://en.wikipedia.org/wiki/Loudspeaker_enclosure#Infinite_baffle |Subwoofer Enclosure Wikipedia Page]]
Kicker Solo-Baric Subwoofer
Experiences in Designing and Building a Subwoofer Enclosure
Hoffman's Iron Law